Imaging apparatus

ABSTRACT

Imaging apparatus for making photoelectrophoretic images by placing a photoelectrophoretic suspension between two or more electrodes while exposing the suspension to activating electromagnetic radiation and an electric field. An electric field may be generated electrostatically either before or during imaging in any manner such as by a corona discharge device or by frictionally rubbing the surface of one of the electrodes.

United States Patent Inventors Leonard M. Carreira l 56] ReferencesCi'ed Penfield; UNITED STATES PATENTS Vsevolod Tulagin, Rochester, bothof, 3,442,781 5/1969 Weinberger 96/1 PP 825,256 3,474,019 10/1969Krieger et al. 96/] Filed May 16, 1969 Division ofSer. No. 561587, June29, 1966, 'f Matthews Assistant Exammer- Robert P. Grelner 3477934Altorne 8 Jam .1 R l b B J K 1 Patented M1814 1971 y es a a ate, arryesse man and David C. Petre Assignee Xerox Corporation Rochester, N.Y.

P' APPAFATPS ABSTRACT: Imaging apparatus for making photoelec- 8 Chums 7Drawing Flgs trophoretic images by placing a photoelectrophoreticsuspen- U.S. Cl 355/3, sion between two or more electrodes whileexposing the 355/4 suspension to activating electromagnetic radiationand an Int. Cl G03g 15/02, electric field. An electric field may begenerated electrostati- G03g l5/00 cally either before or during imagingin any manner such as by Field of Search 355/3, 4, a corona dischargedevice or by frictionally rubbing the surl7; 96/1 face of one of theelectrodes.

1 20 I is, 1/ x l8 4 J Fg I PATENTEu Auswsn SHEET 1 BF 4 3501.483

INVENTOR. LEONARD M. CARREIRA VSEVOLOD TULAGIN Zl/Z'V IMAGING APPARATUSThis is a division of application, Ser. No. 561,587, filed June 29, 1966now U.S. Pat. No. 3,477,934.

This invention relates in general to imaging systems and, morespecifically, to an improved electrophoretic imaging system.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilizes electricallyphotosensitive particles. This process is described in detail and claimin US. Pat. Nos. 3,384,448; 3,384,566 and 3,383,993 all issued on May21, 1968. In such an imaging system, variously colored light absorbingparticles are suspended in a nonconductive liquid carrier. Thesuspension is placed between electrodes, one of which is at leastpartially transparent, and subjected to a potential difference while thesuspension is exposed to an image through partially transparentelectrode. As these steps are completed, selective particle migrationtakes place in image configuration providing a visible image at one orboth of the electrodes. Where the positive image is formed on aconductive transparent electrode, ordinarily the image must betransferred to a receiving sheet so that the relatively expensiveconductive transparent electrode may be reused. An essential componentof the system is the suspended particles which must be electricallyphotosensitive and which apparently undergo a net change in chargepolarity upon exposure to activating electromagnetic radiation, throughinteraction with one of the electrodes. In a monochromatic system,particles of a single color are used, producing a single colored imagesimilar to conventional black and white photograph. In a polychromaticsystem, the images are produced in natural color because mixtures ofparticles of two or more different colors which are each sensitive tolight of a specific wavelength or narrow range of wavelengths are used.Particles used in this system should have both intense pure colors andbe highly photosensitive.

After the exposure and particle migration steps are completed, theelectrodes are separated and the carrier liquid is allowed to evaporate.This leaves images on one or both of the electrodes made up ofselectively deposited particles. Since these electrodes may consist ofrelatively expensive materials or may be integral parts of the imagingapparatus, it is generally required that the images be transferred to areceiving sheet, fixed thereon for later viewing use. This permits theoriginal electrodes to be reused immediately to produce further images.

in order to produce an electric field across the suspension during theimaging process, the transparent electrode generally has a conductivesurface, such astin oxide and the other electrode has a relativelyinsulating surface behind which is a second conductive electrode. Thisprocess is capable of producing excellent color images. However, itwould be desirable to simplify the process by eliminating the need totransfer images produced from an electrode to a receiving sheet. But, itis not generally possible to fix a formed image directly on theconductive transparent electrode since these materials are expensive andmust be reused to provide reasonable economy in the imaging process.Also, these material, e.g., tin oxide coated glass,are often notsuitable for later handling and use even if it is possible to fix animage to the surface thereof. Also, in a reusable system, there areproblems in balancing the requirements of conductivity and transparencyin an electrode. Often, materials which impart conductivity to theelectrode impair transparency. Thus, there is a continuing need forimproved electrode materials for use in electrophoretic imagingprocesses of the sort described above.

In some instances it may be preferable to transfer the reformed imagefrom the electrode. surface to a receiving sheet. For example, where theelectrode upon which the image is formed is transparent, it may bedesirable to transfer the formed image to an opaque viewing sheet suchas paper. The preferred method of transferring the images is to do soelectrophoretically. In this transfer process, immediately after theimaging process, the electrodes are separated and a receiving sheet isbrought into contact with the imaged electrode. The imaging surface isilluminated with white light, causing an electrophoretic migration ofthe image particles to the receiving sheet. The receiving sheet is thenstripped away, carrying with it the image. Where the transfer step iscarried out immediately after the imaging step, effective transfer ofthe image to the receiving sheet is obtained. Where there is a delay ofmore than a few seconds, however, even with the application ofadditional carrier liquid to the image, the quality of the transferredimage is drastically reduced. Density and color balance are degraded andirregularities or blotches are observed in the image areas.

Any time variation between image formation and image transfer introducesvariations into the quality of the final image. Simple nonautomatedcopying devices where the various steps are carried out more or less byhand, the timing of the imaging and transfer steps will inherently vary.Thus, there is a continuing need for an improved method of transferringelectrophoretic images to receiving sheet at varying times after imageformation while maintaining uniform image quality.

It is, therefore, an object of this invention to provide anelectrophoretic imaging system overcoming the above-noted disadvantages.

It is another object of this invention to provide an electrophoreticimaging system capable of producing final images of uniform highquality.

It is another object of this invention to provide an improved method oftransferring electrophoretic images to receiving sheets.

It is another object of this invention to improve the uniformity offinal images produced in an electrophoretic imaging system.

It is still another object of this invention to provide anelectrophoretic imaging system which does not require conductivetransparent electrodes.

It is still another object of this invention to provide an extremelysimple, noncomplex electrophoretic imaging system.

The foregoing objects and others are accomplished in accordance withthis invention by providing in an electrophoretic imaging processwherein the layer of suspension is subjected to an applied electricfield between two electrodes, at least one of which is transparent,while an image is projected onto the suspension through said transparentelectrodes to form an image on one of said electrodes, the step ofelectrostatically charging at least one of said elements, namely anelectrode, the suspension, or the formed image.

In one embodiment of this invention, neither of the two electrodes isconductive and the electrostatic charging step is performed on one ofthe electrodes immediately before the suspension is placed between theelectrodes. The second electrode is held at a potential opposite in signto that of the electrostatic charge placed on the first electrode whilean image is projected on the suspension through the transparentelectrode. The electric field between the charged first electrode andthe second electrode in combination with the photosensitive particles inthe suspension enables an electrophoretic migration to take place inimage configuration. The image formed on one electrode consists ofparticles loosely bonded to the surface. This image may be fixed by anyconventional method. This imaged electrode may be removed from thesystem for later use or viewing. Since this electrode may be anysuitable insulating material, it may be easily and quickly replaced witha fresh sheet and the imaging steps repeated.

in another embodiment of this invention, an electrophoretic image isformed on the injecting electrode, the formed image surface iselectrostatically charged, and the image is transferredelectrophoretically to a receiving sheet. Where the formed image iselectrostatically charged before the transfer step, the quality of thetransferred image is consistently high despite varying or extendedperiods between the image formation and the image transfer steps.

In a further embodiment of this invention, the particle suspension iscoated onto one electrode and the suspension is electrostaticallycharged just before the second electrode is brought into contact withthe suspension and during the imaging step. The second electrode is heldat a potential opposite in sign to that of the electrostatic chargeimposed on the suspension. This charging step has been found to increaseimage density and uniformity.

In a further embodiment of this invention, the two electrodes arebrought into contact with the particle suspension before electrophoreticimaging. The surface of the blocking electrode not in contact with thesuspension is then electrostatically charged. This eliminates therequirement for a power supply to impose a constant potential on theback of blocking electrode during imaging. This simplifies the equipmentnecessary for electrophoretic imaging without lowering image quality.

The uniform electrostatic charging of one or more elements of theelectrophoretic imaging system as described in the different embodimentsabove, may be performed by any conventional means. Charging by coronadischarge is preferred since a uniform charge of the desired potentialmay be simply and easily laid down on a surface without physical contactwith said surface. Charging by corona discharge is described in detailby Carlson in U.S. Pat. No. 2,588,699 and Walkup in U.S. Pat. No.2,777,557. Any other suitable charging methods may be used wheredesired. For example, where a surface such as the injecting or blockingelectrode will not be harmed by physical contact therewith, the surfacemay be charged by rubbing a triboelectrically suitable material thereagainst, as described by Carlson in U.S. Pat. No. 2,297,691.

Images may be formed by the above-described processes from suspensionsof any suitable photosensitive particles. The photosensitive particlesmay, for example, comprise the materials disclosed in U.S. Pat. No.3,383,993 issued on May 21, 1968. Where a monochromatic image is to beformed, the particles will be of a single color. Where polychromaticimages are to be formed, particles of two or more colors may be used.For example, for subtractive color formation, the particles willordinarily be magenta, cyan and yellow. Any suitable insulating liquidmay be used as the carrier for the photosensitive particles and theimaging suspension. Typical insulating carrier liquids include: decane,dodecane, molten paraffin, molten beeswax or other molten thermoplasticmaterials, Sohio Odorless solvent 3440 (a Kerosene extraction availablefrom Standard Oil Company of Ohio), Isopar G (a long-chain saturatedaliphatic hydrocarbon available from Humble Oil Company of New Jersey)and mixtures thereof. The blocking electrode, the surface of thetransfer rollers, and the injecting electrode as shown in FIG. 3 maycomprise any suitable insulating material. Typical materials havingsuitable insulating properties include: Baryta paper (paper coated withbarium sulfate in a gelatin binder), cellulose acetate or polyethylenecoated papers, polyethylene terephthalate, polytetrafluoroethylene,polystyrene, polyamides, etc. In an embodiment such as that shown inFIG. 5, the blocking electrode may be transparent and the imagingsuspension may be exposed through the blocking electrode rather thanthrough the injecting electrode.

The advantages of utilizing uniform electrostatic charging in anelectrophoretic imaging system will become further apparent uponconsideration of the following detailed disclosure of the invention;especially when taken in conjunction with the accompanying drawingswherein:

FIG. 1 shows a simple schematic representation of an electrophoreticimaging system which does not include the electrostatic chargingmovement of this invention;

FIG. 2 shows an exemplary electrophoretic imaging system in which thesuspension is electrostatically charged before imaging;

FIG. 3 shows an exemplary electrophoretic imaging system in which aninsulating injecting electrode is uniformly electrostatically chargedbefore imaging;

FIG. 4 shows an alternative method'of uniformly electrostaticallycharging the injecting electrode as in FIG. 3;

. blocking electrode in the configuration shown in FIG. 5; and

FIG. 7 shows an exemplary method for transferring an electrophoreticimage wherein the formed image is electrostatically charged beforetransfer.

The same numbers are used to designate similar elements throughout thevarious figures.

Referring now to FIG. 1, there is shown an exemplary em bodiment of asystem for forming a photoelectrophoretic image on one of the imagingelectrodes and then transferring the formed image to a receiving sheet.In FIG. 1 there is shown a transparent electrode generally designated 1,which, in this exemplary instance, is made up of a layer of opticallytransparent glass 2 overcoated with a thin, optically transparent layer3 of tin oxide, commercially available under the name NESA glass. Thiselectrode shall hereafter be referred to as the injecting electrode.Coated on the surface of injecting electrode 1 is a thin layer 4 offinely divided photosensitive particles, dispersed in an insulatingliquid carrier. The term photosensitive for the purposes of thisapplication refers to the properties of a particle which once attractedto the injecting electrode, will migrate away from it under theinfluence of an applied electric field when it is exposed to actinicelectromagnetic radiation. For a detailed theoretical explanation of theapparent mechanism of operation of the imaging process, see theabove-mentioned U.S. Pat. Nos. 3,384,488; 3,384,566 and 3,383,993; thedisclosure of which are incorporated herein by reference. Adjacent tothe liquid suspension 4 is a second electrode 5, hereinafter called theblocking electrode, which is connected to one side of. a potentialsource 6 through a switch 7. The opposite side of potential source 6 isconnected to ground, as is injecting electrode 1 so that when switch 7is closed, an electric field is applied across the liquid suspension 4between electrodes 1 and 5.

During the imaging operation, blocking electrode 5 is moved across thesurface of injecting electrode 1. An image projector made up of a lightsource 8, a transparency 9, and a lens 10 is provided to expose theliquid suspension 4 to a light image of the original transparency 9 tobe reproduced. Electrode 5 is made in the form of a roller having aconductive central core 11 connected to the potential source 6. The coreis covered with a layer of a blocking electrode material 12 which may beBaryta paper or other suitable material. An image is formed from theparticle suspension by exposing the particle suspension to the image tobe produced while a potential is applied across the blocking andinjecting electrodes by closing switch 7. Roller 5 is caused to rollacross the top surface of injecting electrode 1 with switch 7 closedduring the period of image exposure. The light exposure causes particlesoriginally attracted to electrode 1 to migrate through the carrierliquid and adhere to the surface of the blocking electrode 5, leavingbehind a pigment image on the injecting electrode surface which is aduplicate of the original transparency 9. Preferably, the particulateimage formed on the surface of injecting electrode 1 is transferred to areceiving sheet and fixed thereon for further use and viewing. Asdescribed in copending application, Ser. No. 542,050 filed Apr. 2, 1966,a transfer roller may be utilized to receive the image from theinjecting electrode surface. Such a transfer roller is shown at 13.Transfer roller 13 has the same general structure as blocking electrode5. A conductive core 14 is connected to ground through a potentialsource 15 and switch 16. The surface of the transfer roller comprisesany suitable material 17, such as Baryta paper, for'receiving the image.The potential imposed on the transfer roller is opposite in sign to thatused on the blocking electrode during the imaging step. While transferroller 13 is passing across the surface of injecting electrode 1,

the image areas are light exposed, either to white light,

suitably filtered white light or to the original image projected throughtransparency 9. Where desired, the surface of the particulate image onthe injecting electrode may be moistened with additional carrier liquidto improve the transfer step. Where transfer roller 13 is passed acrossthe surface of injecting electrode 1 immediately after the image isformed, effective transfer of a good quality image to the surface ofroller 13 is accomplished. However, if an appreciable delay of more thana few seconds occurs between the imaging and the transfer steps, thequality of the transferred image decreases.

Images produced by systems of the sort schematically shown in FIG. 1 aregenerally of excellent quality. However, the system as shown in FIG. 1requires a conductive transparent injecting electrode which is generallyrather fragile and expensive and, thus, necessitates the transfer of theimage to a receiving sheet for further use in viewing. Also, imagetransfer must be accomplished immediately after image formation in orderto obtain a good image on the receiving sheet. This imaging system maybe substantially improved by the use of electrostatic charging ofvarious elements of the system during the imaging and transferoperation. FIGS. 2-7 show various embodiments of this improvedelectrophoretic imaging system. Y

Referring now to FIG. 2, there is shown a modification of the system ofFIG. 1 in which an image of improved density and color balance is formedon the injecting electrode surface. In this instance, however, a coronadischarge unit 18 is arranged to pass across the surface of theinjecting electrode immediately prior to the imaging step. The coronahead 18 is connected to ground through potential source 19 and switch20. Since injecting electrode 1 is also grounded, as corona unit 18passes across the surface of the injecting electrode with switch closed,a uniform electrostatic charge is deposited on the surface of suspension4. This electrostatic charge is of the same sign as the potentialimposed on the blocking electrode when it passes across suspension 4during the imaging step. It appears that this preliminary electrostaticcharge enhances the ability of light-struck particles to migrate, thusresulting in an image of improved density and color balance.

FIG. 3 shows a further embodiment of the use of uniform electrostaticcharging in photoelectrophoretic imaging systems. This embodimentdiffers from that shown in FIG. 1 in that the formed image is fixeddirectly onto a removable injecting electrode, thus eliminating therequirement for a transfer roller 13. In this embodiment, the injectingelectrode 1 includes a sheet of insulating material 21 which isuniformly electrostatically charged as by corona unit 18 immediatelybefore the imaging operation. Insulating sheet 21 may comprise anypartially transparent insulating material, such as Mylar (polyethyleneterephthalate, available from DuPont). The electrostatic charge placedon the surface of sheet 21 is opposite in sign to that imposed on theconductive center of blocking electrode 5. In the system shown in FIG.3, the particulate suspension 4 is shown as coated on the surface ofblocking electrode 5. While this is often convenient, the suspension maybe coated on the surface of sheet 21 immediately after its surface hasbeen charged by corona means 18. During the imaging step, as blockingelectrode 5 passes across the surface of sheet 21, a positive imagecorresponding to transparency 9 is formed on the surface of sheet 21.This image may be fixed by any convenient means, such as by a binderincluded in the particle carrier liquid, by laminating a second sheetover the formed image, by spraying with a suitable lacquer, or by athermoadhesive layer on the surface of sheet 21 such as is described incopending application, Ser. No. 459,860, filed June 28, l965. Theembodiment shown in FIG. 3 has the distinct advantage over that shown inFIG. 1 in that the image need not be transferred to a receiving sheet.Any transfer step necessarily involves some loss of image quality. Also,this system lends itself to rapid production of multiple copies in thatone need only replace imaged sheet 21 with another sheet and recoatsuspension 4 onto electrode 5 to be ready for subsequent imaging.

FIG. 4 shows the embodiment of FIG. 3 with an alternative method ofcharging the insulating injecting electrode surface. Here, theinsulating sheet 21 is charged by means of a rotating fur brush 22 whichis passed across the surface of sheet 21 immediately before imaging.Such triboelectric charging is described in detail by Carlson in U.S.Patent No. 2,297,691.

The sheet 21 and brush 22 materials are selected so as totriboelectrically charge the surface of sheet 21 to a potential having asign opposite to that imposed on the core of blocking electrode 5. Thisalternative has the advantage in simplifying the system by eliminatingthe need for corona head 18, power supply 19, and switch 20.

FIG. 5 shows a further embodiment of electrophoretic imaging utilizingelectrostatic charging in which the blocking electrode material 12 asshown in FIG. 1 is placed in direct contact with the particlessuspension 4 and power supply 6 connected to conductive backing isreplaced with uniform electrostatic charging of the upper surface of theblocking electrode. In this embodiment, the particle suspension 4 iscoated on the surface of injecting electrode 1 as in the embodiment ofFIG. 1. A projection system comprising lamp 8, transparency 9 and lens10 is positioned so as to project an image of suspension 4. In thisembodiment a sheet of blocking electrode material 23 is placed over thesuspension 4 and the upper surface of sheet 23 is uniformlyelectrostatically charged by means of corona head 18 supplied with apotential by power supply 19 through switch 20. An electric field isimposed on the suspension since the injecting electrode is grounded.

Sheet 23 may comprise any suitable insulating material, such as Barytapaper, Mylar (polyethylene terephthalate) etc. In this system the backof sheet 23 is charged, and the suspension is exposed to an image. Sheet23 is then removed, leaving a positive image conforming to the originalon the surface of the injecting electrode. When it is desired totransfer this image to a receiving sheet, a second insulating sheet 23is placed over the formed image and corona means 18 is again passedacross the back of sheet 23 to uniformly electrostatically chargeitQI-Iowever, for the transfer operation the sign of the electrostaticcharge placed on 23 is opposite to that used during the imaging step.When this second sheet 23 is stripped from injecting electrode 1, theformed image will be found to have transferred to sheet 23 and may befixed thereon by any suitable method. This embodiment is asimplification of that shown in FIG. 1 in that the multilayered rollerelectrode 5 is replaced by a single sheet 23 and a corona dischargeunit.

FIG. 6 shows an embodiment generally similar to that of FIG. 5 in whichthe back of sheet 23 is charged triboelectrically by means of a rotatingfur brush 22 instead of the corona discharge unit. Where a secondtransfer step is desired as described above in the description of theembodiment of FIG. 5, it may be desirable to select the fur brushes usedduring the imaging step and during the transfer step so as totriboelectrically charge the surface of sheet 23 to potentials ofopposite sign during imaging and transfer steps. This system is afurther simplification of that shown in FIG. 5 in that corona chargingunit 18, power supply 19, and switch 20 are replaced by a simplerotating fur brush.

FIG. 7 shows an embodiment of the system shown in FIG. 1 in whichtransfer of a formed electrophoretic image is improved. The system asused in this embodiment is generally the same as that shown in FIG. 1,except that a corona discharge unit comprising a corona head 18,potential source 19 and switch 20 is positioned between the blockingelectrode roller 5 and the transfer roller 13. After blocking electroderoller 5 has passed across the surface of the injecting electrode duringthe image forming step, corona head 18 is passed across the formed imageto electrostatically charge the surface of the formed image to apotential opposite to that imposed on the transfer roller. Wheretransfer takes place within a few seconds after imaging theelectrostatic charging of the formed image results in somewhat improveddensity in the transferred image, i.e., more complete transfer ofparticles from the surface of the injecting electrode 1 to transferroller 13. Where there is delay of more than a few seconds betweenimaging and transfer, the image quality falls off drastically where theformed image is not electrostatically charged before transfer. However,where the formed image is charged before transfer, quality of thetransferred image remains high despite substantial delays betweenimaging and transfer. Where there is appreciable delay between imageformation and transfer, it may be desirable to moisten the surface ofthe formed image with a small amount of the carrier liquid.

Good quality images may be produced with voltages imposed on theblocking electrode and on the transfer roller in the range from about300 to 5,000 volts in the various embodiments of this invention. Imagesof high quality may be produced with potentials of about 2,000-4,000volts without danger of undesirable air ionization. Therefore, apotential of about 3,000 volts is preferred. A corona discharge voltagemay be in the range from about 4,000 to 8,000 volts. A

. preferred corona voltage is about 6,000 volts since this results inmost effective image formation and transfer. Where the various elementsare charged triboelectrically, the charging member may comprise anysuitable material which is spaced from the material to be charged on thetriboelectric series such as to produce a charge on the element of thedesired sign.

The following examples further specifically define the present inventionwith respect to the use of uniform electrostatic charging inelectrophoretic imaging systems. Parts and percentages are by weightunless otherwise indicated. Examples below are intended to illustratevarious preferred embodiments of the invention and of the differentembodiments described above.

All the following examples are carried out in apparatus of the generaltype illustrated in the various figures. Where blocking electrodes inroller form or transfer rollers are used, the rollers are approximately2%inches in diameter and are moved across the plate surface of about 1.5centimeters per second. In each case, the injecting electrode surfaceemployed is roughly 3 inches square and is exposed with a lightintensity of about 8,000-foot candles as measured on the uncoatedinjecting electrode surface. Where a monochromatic image is to beproduced, the suspension is exposed to an image by means of aconventional black and white transparency. Where a polychromatic imageis to be produced, the suspension is exposed to an image by means of aColor transparency. All pigments which have a relatively large particlesize as received commercially or as made are ground in a ball mill forabout 48 hours to reduce their size to provide a more stable dispersionand to improve the resolution of final images.

EXAMPLE I This example is performed with an imaging system of the sortshown in FIG. 1. About eight parts of 2, 4, 6-tris (3 pyrenylazo)phloroglucinol, prepared as described in U.S. Pat. No. 3,384,632 issuedon May 21, 1968 is mixed with about 100 parts Sohio Odorless Solvent3440, a kerosene fraction available from The Standard Oil Company ofOhio. This dispersion is coated onto the NESA glass substrate. Anegative potential of about 2,500 volts is imposed on the rollerelectrode during exposure. After exposure, an image corresponding to theoriginal is seen on the NESA surface. Immediately after image formationa transfer roller having a Baryta paper surface and subjected to apositive potential of about 2,000 volts is passed across the NESA glasswhile the original image is projected onto the NESA surface. The imageis transferred to this roller surface from the NESA electrode. Theblack-onwhite image produced is of good quality. A small proportion ofthe black particles remain on the NESA surface must be cleaned therefrombefore subsequent imaging operations.

EXAMPLE [I The imaging and transfer steps of example I are repeatedexcept that immediately prior to imaging a corona discharge unit ispassed across the particle suspension, depositing a uniform positivecharge of about 6,000 volts on the suspension. The imaging and transfersteps are then performed as in example I.

The resulting image is of excellent quality and somewhat greater densitythan that produced in example I.

EXAMPLE m The imaging and transfer steps of example I are repeated,except that the particle suspension comprises about three parts Algolyellow GC, 1,2,5 ,6-di(c,c'-diphenyl)thiazoleanthraquinone, C.I. No.67,300, available from General Dye Stuffs; about three parts of amagenta pigment, Watchung Red B, 1(4'-methyl-5'-chloroazobenzene-2'-sulfonic acid)-2- hydroxy-S-napthoic acid, C. I. No. 15,865,available from E. I. duPont de Nemours; and about three parts of a Cyanpigment, Monolight Fast Blue GS, a mixture of alpha and beta metalfreephthalocyanine, available from the Arnold Hoffman Co. The image producedis of good quality with good color balance.

EXAMPLE IV An image is formed as in example III except that a coronadischarge unit is passed across the suspension immediately before theimage forming step to deposit a uniform electrostatic charge having anegative potential of about 6,000 volts on the suspension. The image isthen formed and transferred to a receiving sheet as in example III. Theimage is of excellent quality with density and color balance improvedover the image formed in example lII.

EXAMPLE V This example uses an electrophoretic imaging system such as isshown in FIG. 3. A IO-micron sheet of Mylar, a polyethyleneterephthalate film available from E. I. duPont de Nemours is placed incontact with the conductive surface of the injecting electrode. Asuspension is formed comprising about seven parts of2,4,6-tris(3'-pyrenylazo)-phloroglucino1, in about parts Isopar G, along chain saturated aliphatic hydrocarbon available from The Humble OilCompany of New Jersey. This suspension is coated onto the blockingelectrode surface to a thickness of about 5 microns. A corona chargingunit is then passed across the Mylar sheet uniformly electrostaticallycharging the sheet to a negative potential of about 4,000 volts.Immediately thereafter the coated blocking electrode is passed acrossthe Mylar sheet while subjected to a positive potential of about 2,500volts. After the blocking electrode has passed across the Mylar sheet animage is seen on the Mylar sheet corresponding to the original. Thisimage is of good quality, approximately equal to that produced inexample I.

EXAMPLE VI The imaging steps of example V are repeated except that theMylar sheet is charged by a fur brush such as is shown in FIG. IVinstead of by corona discharge. The surface electrostatic potentialimposed on the Mylar sheet is negative and about 3,000 volts. The imageis then formed as in example V. An image of good quality correspondingto the original results on the Mylar sheet.

EXAMPLE VII The imaging steps of example V are repeated except that thepigment suspension comprises about three parts of a yellow pigment,8,13-dioxodinaphtho-( 1,2-2',3 )-furan-6-carbon- 4"-methoxy anilide,prepared as described in copending application, Ser. No. 421,377, filedDec. 28, 1964; about three parts of a magenta pigment, Napthyl Red B,1-(2-methoxy- Snitrophenylazo)-2 hydroxy-3"-nitro-3-naphthanilide, C.I.No. 12,355, available from Collway Colors; and about three parts of aCyan pigment, Cyan Blue GTNF, the beta form of copper phthalocyanine C.I. No. 74,160, available from Coll way Colors dispersed in about 100parts Sohio Odorless Solvent 3440. This suspension is coated onto theblocking electrode surface, the Mylar sheet is corona charged and thequality corresponding to the original is formed on the surface Ser. No.445,240, filed Apr. 2, 1965; and about three parts of a-Cyan pigment,Diane Blue, 3,3'-methoxy-4,4'-diphenyl-bis(l"-azo-2"-hydroxy-3"-naphthanilide, C]. No. 21,180, available fromHarmon Colors, dispersed in about 100 parts Sohio Odorless Solvent 3440.This mixture is coated onto the Baryta surface of the blockingelectrode, the surface of the injecting'electrode is corona charged to anegative potential of about 4,000 volts, and the blocking electrode ispassed across the Lucite sheet under a positive potential of about 2,500volts as in example VII. A full color image conforming to the originalis left on the surface of the Lucite sheet. A 5-micron sheet of Mylarfilm is laminated over the image surface to fix the image. The imagedsheet is then removed and replaced with a fresh Lucite film. The imagingmix is recoated on the blocking electrode surface and another image isproduced as described above.

EXAMPLE VIII This example is performed with an electrophoretic imagingsystem of the sort shown in FIG. 5. A pigment suspension comprising ofabout seven parts of Monolite Fast Blue GS, dispersed in about 100 partsSohio Odorless Solvent 3440 is coated onto the injecting electrodesurface to a thickness of about 5 microns. A l-micron Mylar sheet isthen placed over the suspension in intimate contact therewith. The freesurface of the Mylar sheet is then chargedv by corona to a negativepotential of about 4,000 voltsfA black and white image is projected ontothe suspension through the injecting, electrode. The Mylar sheet is thenstripped from the suspension leaving an image on the injecting electrodecorresponding to the original of satisfactory quality.

EXAMPLE ix This example uses an electrophoretic imaging system such asis shown in FIG. 5. A pigment suspension is prepared comprising aboutthree parts of a yellow pigment, Indofast Yellow Toner, flavanthrone,C.I. No. 70,600, available from Harmon Colors; about three parts of amagenta pigment, Quindo Magenta RV-6803, a substituted quinacridoneavailable from Harmon Colors; and about three parts of a Cyan pigment,Monolite Fast Blue GS, a mixture of the alpha and beta forms ofmetal-free phthalocyanine, available from theArnold Hoffman Company,dispersed in about 1001 parts Sohio Odorless Solvent 3440. Thissuspension is coated onto the injecting electrode surface to a thicknessof about microns. A sheet of Baryta paper is then placed over thesuspension. with the coated paper surface in contact with thesuspension. The back of the Baryta paper is then uniformlyelectrostatically charged to a negative potential of about 2,000- voltsby a corona discharge means. The suspension is then exposed to a fullcolor image and the Baryta paper is stripped away. A full color imagecorresponding to the original remains on the injecting electrodesurface. A second sheet of Baryta paper is then placed over the formedimage and the back of the sheet is charged to a positive potential ofabout 2,000 volts while the image is again projected onto the injectingelectrode surface. When the Baryta paper is stripped away it is foundthatthe image has transferred to the Baryta paper surface.

EXAMPLE X The imaging steps of example VIII are repeated, except thatthe back of the Mylar sheet is uniformly electrostatically charged bymeans of a rotating fur bmsh instead of by corona discharge. Thetriboelectric charging is to a negative potential of about 3,000 volts.The image is then formed and the electrodes separated as in exampleVIII. An image of good quality corresponding to the original results.

EXAMPLE XI This example uses an electrophoretic imaging system such asis shown in FIG. 7. About eight parts of 2,4,6-tris (3'- pyrenylazo)phloroglucinol is mixed with about parts Sohio Odorless Solvent 3440 andthe suspension is coated onto the NESA glass substrate to a thickness ofabout 5 microns, A negative potential of about 2,500 volts is imposed onthe blocking electrode during exposure. After exposure, an imagecorresponding to the original is seen on the NESA surface. Immediatelyafter image formation a second roller having a Baryta paper surface andsubjected to a positive potential of about 2,000 volts is passed acrossthe NESA surface while the original image is projected onto the NESAsurface. The image is transferred to this roller surface from the NESAelectrode. The black-on-white image produced is of good quality andcorresponds to the original. A small amount of the black particlesremain on the NESA surface and must be cleaned therefrom beforesubsequent imaging operations.

EXAMPLE XII The NESA electrode is coated, charged, and imaged as inexample XI. However, here immediately before the transfer roller passesacross the NESA surface, a corona discharge means is passed across saidsurface under a negative potential of about 6,000 volts. The imageproduced on the transfer roller is of higher density than in example X1and fewer pigment particles are left on the NESA glass electrode.

EXAMPLE XIII A dispersion is coated onto the NESA electrode and an imageis produced on said electrode as in'example XI. About 5 minutes afterthe image is formed, the image is moistened with Sohio Odorless Solvent3440 and the transfer roller is passed across the NESA electrode. Only asmall proportion of the image particles transfer to the transferelectrode. The image transferred is of low density and very poorquality.

EXAMPLE XIV The NESA electrode is coated, charged and imaged as inexample XIII. I-Iere, however, a corona discharge means is passed acrossthe NESA electrode just before the transfer roller. The corona dischargemeans deposits a uniform negative potential of about 5,000 volts. Theimage transferred is of excellent quality, comparable to that producedin example XI.

EXAMPLE XV About three parts of a yellow pigment, Algol Yellow GC, aboutthree parts of a magenta pigment, Watchung Red B, and about three partsof a Cyan pigment, Monolite Fast Blue GS are dispersed in about 100parts Sohio Odorless Solvent 3440. This dispersion is coated onto theNESA electrode and an image is formed as in example XI. About 5 minutesafter the image is formed, the formed image is moistened with SohioOdorless Solvent 3440 and a transfer roller is passed across the imageunder a positive potential of about 2,500 volts. The image transferredto the roller is of poor quality, of low density, and very poor colorbalance.

EXAMPLE XVI A dispersion is formed, coated onto the NESA ELEC- TRODE andan image is formed as in example XV. About 5 minutes after the image isformed, the image is moistened with Sohio Odorless Solvent 3440 and acorona discharge means is passed across the formed image depositing auniform negative potential of about 4,000 volts on the formed image. Im-

mediately thereafter the transfer roller is passed across the formedimage under a positive potential of about 2,500 volts. The imagetransferred to the transfer roller is of excellent quality, with muchhigher density and better color balance than that produced in exampleXV.

Although specific components and proportions have been described in theabove examples relating to various electrophoretic imaging systemsutilizing uniform electrostatic charging of one element of the system,any of the materials as listed above may be used with similar results.In addition, other materials may be added to the particle suspension orto the various electrodes to synergize, enhance, or otherwise modifytheir properties.

Other modifications and ramifications of the present invention willoccur to those skilled in'the art upon a reading of the presentdisclosure These are intended to be included within the scope of thisinvention.

What we claim is:

1 An imaging apparatus for forming an image from a photoelectrophoreticsuspension including a first electrode,

a second electrode adapted to contact said first electrode through thephotoelectrophoretic suspension appliable between said electrodes,

illumination means to expose the suspension between said electrodes toactivating electromagnetic radiation,

electric field generating means for providing an electric field acrossthe suspension between the electrodes during the exposure of thesuspension to the activating radiation, and

electrostatic charge generating means in close operative proximity to atleast one of said first and second electrodes for depositing a uniformcharge thereon.

2. The apparatus of claim 1 wherein said electrostatic charge generatingmeans is a corona generating device.

3. The apparatus of claim 2 wherein said corona generating device is acorotron.

4. .The apparatus of claim 1 wherein said electrostatic chargegenerating means includes a material for depositing a charge on one ofthe electrodes with which it makes friction contact to improve imaging.

5. The apparatus of claim 1 wherein said first and second electrodeshave insulating layers thereon.

6. The apparatus of claim 5 wherein said electrostatic charginggenerating means is positioned to operate on one of said electrodesprior to the application of the suspension to one of said electrodes.

7. The apparatus of claim 5 wherein said electrostatic charge generatingmeans deposits a charge on one of said electrodes opposite to thepotential of the field supplied by the electric field generating means.

8. The apparatus of claim 1 wherein the electrodes are flat membershaving the suspension coated therebetween and said electric fieldgenerating means includes an electrostatic charge generating means.

2. The apparatus of claim 1 wherein said electrostatic charge generatingmeans is a corona generating device.
 3. The apparatus of claim 2 whereinsaid corona generating device is a corotron.
 4. The apparatus of claim 1wherein said electrostatic charge generating means includes a materialfor depositing a charge on one of the electrodes with which it makesfriction contact to improve imaging.
 5. The apparatus of claim 1 whereinsaid first and second electrodes have insulating layers thereon.
 6. Theapparatus of claim 5 wherein said electrostatic charging generatingmeans is positioned to operate on one of said electrodes prior to theapplication of the suspension to one of said electrodes.
 7. Theapparatus of claim 5 wherein said electrostatic charge generating meansdeposits a charge on one of said electrodes opposite to the potential ofthe field supplied by the electric field generating means.
 8. Theapparatus of claim 1 wherein the electrodes are flat members having thesuspension coated therebetween and said electric field generating meansincludes an electrostatic charge generating means.